Huh, that is interesting. I did not know wyeast had Orval yeast. I guess what is really interesting to me is that whitelabs does (wlp510) but I do not believe their version includes any brett. Only the primary sacchromyces strain.

That said, assuming it is similar to the actual Orval blend here are the numbers from Orval according to Brew Like a Monk.

apparent attenuation 94% (with an OG on their beer of 1.055 (13.6 P)

They pitch around 57 F and it may rise to 72 F for 4 days

It is then held for 3 weeks at 59 F in a secondary vessel with new yeast (including brett)

Referment in bottle with primary yeast for 5 weeks at 59 F; centrifuged, but brett remains and will continue to ferment.

Not sure if that info helps as yeast tends to act differently in a commercial set up vs. small scale homebrew.

Personally I would let it sit in the primary 3 weeks. Check it. If it is way off from your target FG let it sit another week, it won't hurt. If it is close then rack it to a clean carboy or keg (with a airlock rigged) and let it sit until it seems to be done. Meaning, it is at about your estimated FG and has remained that way for a week or more. The brett will keep working but as long as you have most of the readily available sugars fermented their should not be any bottle bombs, assuming you are bottling it. If not, then keg it up. I would think a good amount of aging would do wonders overall.